[BZOJ]1089 严格n元树(SCOI2003)

#include <cstdio>
#include <algorithm>
#include <cstring>
#define MOD 10000
#define MS 400
#define MN 20
using namespace std;
struct hp
{
    int len,a[MS];
    void add() {++a[1];}
    friend hp operator-(const hp& A,const hp& B)
    {
        hp C=A;
        register int i;
        for (i=1;i<=B.len;++i)
        {
            C.a[i]-=B.a[i];
            if (C.a[i]<0) --C.a[i+1],C.a[i]+=MOD;
        }
        while (!C.a[C.len]) --C.len;
        return C;
    }
    friend hp operator*(const hp& A,const hp& B)
    {
        hp C; C.len=A.len+B.len+1;
        register int i,j;
        memset(C.a,0,sizeof(C.a));
        for (i=1;i<=A.len;++i)
            for (j=1;j<=B.len;++j)
                C.a[i+j-1]+=A.a[i]*B.a[j];
        for (i=1;i<C.len;++i)
            C.a[i+1]+=C.a[i]/MOD,C.a[i]%=MOD;
        while (!C.a[C.len]) --C.len;
        return C;
    }
}f[MN],ans;
int m,n;

inline int read()
{
    int n=0,f=1; char c=getchar();
    while (c<‘0‘ || c>‘9‘) {if(c==‘-‘)f=-1; c=getchar();}
    while (c>=‘0‘ && c<=‘9‘) {n=n*10+c-‘0‘; c=getchar();}
    return n*f;
}

hp mi(hp x,int y)
{
    hp z;
    memset(z.a,0,sizeof(z.a)); z.len=z.a[1]=1;
    for (;y;y>>=1,x=x*x) if (y&1) z=z*x;
    return z;
}

int main()
{
    register int i;
    m=read(); n=read();
    if (n<=1) return 0*printf("1");
    f[1].len=1; f[1].a[1]=2;
    for (i=2;i<=n;++i) f[i]=mi(f[i-1],m),f[i].add();
    ans=f[n]-f[n-1];
    printf("%d",ans.a[ans.len]);
    for (i=ans.len-1;i;--i) printf("%04d",ans.a[i]);
}